Selecting the Correct Waterjet Pump

Jeff Schibley of Jet Edge advises that before investing in a waterjet system, the waterjet manufacturer needs to perform a test cut. Using material supplied by the customer, most waterjet manufacturers provide free test cuts.

The test helps determine the number of cutting heads needed to achieve the desired throughput, how much horsepower is necessary to supply the proper amount of water to each cutting head, and the most efficient orifice/nozzle combination, abrasive feed rate, and pressure for a given application.

We cut the part to determine how much energy is required. As an example, you say, a 0.010/0.030 orifice/nozzle combination at 60,000 psi made my part, but not as fast as I want. Well, I can run two 0.010/0.030 nozzles with a 50hp pump or I can run four .010/.030 nozzles with a 100hp pump, or I can run six 0.010/0.030 nozzles with a 150hp pump. If I’m cutting much over ¾” thick material, I’m probably going to want to put a 50hp of energy into that nozzle. I’m going to run at least a 0.010/0.030 at 75,000 psi (5,200 bar) or a 0.015/0.045 at 60,000 psi. Depending on the throughput is how we determine the horsepower, so if I run one head, I need 50hp, if I’m running two heads, I might need 100 hp, if I’m running three, I might want 150hp, if I’m running four, I might want 200 hp to feed the proper amount of water to that nozzle. We’re trying to run as efficient a nozzle setup as we can. In a 0.010/0.030 I can accelerate 0.6 pounds per minute of abrasive at 60,000 psi and I can accelerate 0.7 pounds per minute at 75,000 psi.

Jeff Schibley, Jet Edge

Multi-Head Systems

The quickest way to increase the productivity of a waterjet system is to add multiple cutting heads to the system, Schibley noted.

“Look at most successful job shops and what are they running?” Schibley asked. “They are running two heads, three heads, four heads. That’s generally because we burden a machine with overhead costs and general and administrative costs (G&A) based on that machine. We don’t burden each cutting head, so when we start putting multiple heads on a machine it allows us to prorate our G&A costs over a greater number of parts per cut. So if I have $50 per hour for G&A costs and I’m running one head and I’ve got $37 per hour operating costs, I’ve got $87 in costs and I haven’t made a machine payment yet in operating that single head. Now if I go to two heads, what happens? If I have a 100hp pump and I’m operating two nozzles, I still have my $37 to run each one of them, but my cost per part dropped by $25 because I was able to prorate my overhead costs.”

Mirroring – Cutting Large Parts Twice as Fast

According to Bradley Schwartz, Jet Edge’s Pacific regional manager, adding optional mirroring capabilities to a waterjet system saves a large amount of time. Waterjet operators can cut large parts at the same time with two cutting heads using mirroring capabilities, increasing productivity by two-fold and freeing the labor and machine for other projects.

Precision Waterjet Concepts of Pequot Lakes, Minnesota, saves time and money by mirroring parts with a Jet Edge Mid Rail Gantry system featuring programmable head spacing.

We cut a lot of extremely large parts and we can save a lot of time and money by mirroring. Fifty percent of the time, we are mirroring. The programmable head spacing also saves us 10-15 minutes per job on set up time.

Joe Quaal, President, Precision Waterjet Concepts

Nesting Software – Maximizes Potential

“A good nesting program is very important for any system, especially if you are looking at material that costs quite a lot and you’re doing high volume,” Schwartz said. “You can look at the efficiency of the nesting software and just conservatively see a 5% savings. Nesting will give you a huge amount of cost savings in a year.”

Money is saved using nesting software, and productivity is increased by maximizing the amount of parts that can be cut out of a piece of material. Using this strategy, the downtime is minimized during loading and unloading of parts, and waste is reduced.

The software can also be employed to tab parts in order to prevent them from falling into the waterjet tank. The software also helps to keep the parts together in a sheet of material, so that loading and unloading can be sped up by removing the entire sheet at once.

Arro-Jet Engineering and Consulting of Camarillo, California, offers an example of how shops can save money using nesting and pass the savings on to customers.

One of Arro-Jet's customers wanted to have parts cut from 20 84"X40" 3" thick titanium plates valued at $50,000 a plate. The customer’s expectation was to get nine parts from each plate. However, Arro-Jet tightly nested the parts and had 10 parts cut from each plate, which left the customer with 20 additional parts that they did not expect.

Pneumatic Drill

Schwartz explained that pneumatic drills are a cost-effective accessory to speed up waterjet processing time, and can be used for pre-drilling material that is sensitive to delamination, such as fiberglass or polycarbonate.

The programming sequence first runs the drill, pre-drilling at the desired locations, and then switches to the waterjet to finish the part. Productivity is increased as waterjet operators can quickly pre-drill and cut sensitive material, and avoid employing a long lead in cut or slower low-pressure pierce cut to the part. The programming also allows waterjet shops to cut materials that may have been avoided in the past because of delamination concerns.

Height Sensing

A contact height sensor can be an invaluable waterjet accessory for avoiding system shutdown to replace a nozzle after slamming into a tipped up part or uneven material.

According to Schwartz, waterjet operators can overcome significant fluctuations in material flatness using contact height sensors and maintaining a constant automatic standoff from the material. Accordingly, waterjet operators can achieve optimum cut quality, taper, tolerance, and speed without the need to monitor the standoff.

By programming height sensors, previously cut parts that may have tipped up after being cut, can be avoided. Schwartz added that height sensors are also essential in running underwater cutting operations as the operator cannot monitor the “stand off distance” between the material and nozzle.

In dual pressure cutting, we want the ability to peck our way through material ever so gently with lower pressure water, and then as we get that hole in there, we can increase the pressure. In the case of glass, if I impact glass with 60,000 psi water, I’m going to get chips just like I’d get on my windshield when I’m driving behind a gravel truck and it throws a stone at me. It’s going to take a big chunk out of it. I don’t want to make that big chunk. I want to cut gently through there. Non-tempered glass cuts fine as long as we cut through from an edge, so we peck a tiny hole in there and now we can boost to high pressure. But when you take a waterjet pump and you ramp that pressure up and down, what occurs? Number one, when we ramp and load up and down on the electric motor it causes it to use more electricity. It also causes us to fatigue our high pressure components faster. High pressure components are designed to be at maximum pressure. They like being at 60,000 psi, or 75,000 psi, or 40,000 psi, whatever your system runs at. What they don’t like is being at that pressure and suddenly being depressurized. It’s that action that creates fatigue.

Jeff Schibley, Jet Edge

Schibley explained that Jet Edge’s patented Dual Pressure Valve® helps to overcome the wear and tear of dual pressure cutting, and can be used with any waterjet system. Using the valve, waterjet operators can increase and decrease water pressure independent of the waterjet pump.

“This allows us to reduce the pressure at the cutting head without having to ramp our pump up and down,” Schibley explained. “So all the plumbing out to the cutting head gets to stay at what it likes to be at and what it’s designed to be at, ultra-high pressure, and it reduces wear and tear.”

Since adding a Dual Pressure Valve, Creative Edge Master Shop, Inc. of Fairfield, Iowa, has seen its downtime and maintenance costs reduced and productivity increased.

The waterjet fabrication and design company runs nine waterjet systems for more than 80 hours a week in order to cut intricate pieces of mostly stone and tile for custom flooring designs that can be seen in fine homes, civic institutions, and commercial buildings, around the world.

Such delicate cutting requires altering of high-low water-pressure settings as many as 200 times a day by the company’s waterjet operators. This process takes 10 seconds per cycle and puts a huge strain on the intensifier pump that is used to power the waterjet, and on the connecting high-pressure hoses.

Ten seconds times 200 cycles per shift adds up to significant production gains, especially when you consider that we cut many small parts that may only take 30 seconds in actual profile cut time. If you're doing lots of high-low cycles, you are stressing every component. On one machine, I was replacing blown lines every week. Every week, I would have a leak somewhere and would have to spend $200 an hour for maintenance.

Mark McCabe, Engineer, Creative Edge

However, according to McCabe, after installing the Jet Edge Dual Pressure Valve, there has been no need to service the offending intensifier pump, which has led to increased productivity by eliminating downtime between high-low cycles.

"That Dual Pressure Valve is amazing," he said. "It has just been a trooper. Nobody else has anything comparable on the market. It saves wear and tear on all the components."

This information has been sourced, reviewed and adapted from materials provided by Jet Edge, Inc.

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